Heat blowers



Jan. 7, 1958 P. E.NOKES ET AL HEAT BLOWERS 2 Sheets-SheetR Filed March 26, 1956 oo upm fN "5w ova vmfiw h; W MW m 3 Q United States Patent HEAT BLOWERS Philip E. Nokes, Chester E. Rogers, Jr., and Harry E.

Dow, Beverly, Mass., assignors to United Shoe Machinery Corporation, Boston, Mass., a corporation of New Jersey Application March 26, 1956, Serial No. 573,992 4 Claims. (Cl. 219-39) This invention relates to air heating devices and more specifically it relates to electrically operated apparatus of the type commonly referred to as heat blowers for providing a stream of heated air.

A common use for such heat blowers is the removal of wrinkles in the upper leather around the periphery of a lasted shoe. In such service, use of the apparatus is usually intermittent. Additionally, the temperature of the efiiuent air is somewhat critical since it must be hot enough to shrink the leather but not so hot as to burn it. Although changes in the temperature of the heated air can be compensated for in some degree by varying the length of time during which the leather is subjected thereto, it nevertheless is desirable that the air temperature remain within predetermined limits during the course of operation whether it be on one shoe or upon a plurality of shoes. Accordingly, either the operator must keep the heat blower running continuously, which is uneconomical, or else he must wait after starting the heat blower until it has attained thermal equilibrium.

Heating blowers of known type are commonly slow to attain such equilibrium either by reason of ineflicient heat exchange design requiring a mass of exterior insulation to minimize heat losses arising progressively with the temperature of the blower, or else by reason of the incorporation in the design of a large mass of inert material in the interior of the heat exchanger, for example, a ceramic core on which the heat element is wound and which must be brought up to temperature before stable operation is achieved.

Accordingly, it is an object of the invention to provide an improved heat blower which efliciently utilizes the heat provided by a heating element and which reaches thermal equilibrium in a minimum length of time after being turned on.

To this end and in accordance with a feature of the invention, the illustrative heat blower, which is of the coaxial tube heat exchanger type in which the air traverses a train of serially communicating passages formed by nested tubes of different diameters within an outer casing from the outermost tube to the innermost tube and out a nozzle, depends entirely upon the air stream for keeping the outer casing cool enough to be touched and not to radiate excessive heat, while the heating element is of the metallic sheathed conductor wire type and is Wound, not on a ceramic core, but in substantial contact with and about the innermost tube through which the air stream passes just before leaving the blower. In order that the air stream may provide adequate cooling for the casing to permit it to be touched, at least two passages are provided outside the tube adjacent to the exterior of the heating element.

In accordance with another feature of the invention contributing to the localization of the maximum heat exchange at the heating element, the element is formed as a one-layer helical winding confined between the innermost tube and the next adjacent tube to induce the 2,819,373 Patented Jan. 7, 1958 2 air stream passing between said tubes into a helical path to provide a maximum of surface contact between the air and the element and thereafter contact of the air with the inside of the innermost tube.

Another object of the invention is to provide a heat blower which is simple and convenient to maintain and can readily be taken apart for cleaning or replacement of a heating element.

To this end and in accordance with another feature of the invention, the heat exchanger portion of the blower comprises a cylindrical casing having spaced wall members forming a chamber within the casing, while the tubes of the exchanger are carried at one end only, in order of decreasing diameter, alternately by one and the other of the wall members so that the wall members with their tubes may readily be separated for cleaning from a disposition in which the tubes are supported in nested relation to ,form a continuous passage for an air stream alternating in direction of flow lengthwise of the tubes from one passage to the next inner passage.

Other features and advantages of the invention will best be understood from the following description taken in connection with the appended drawings in which:

Fig. 1 is a side elevation of an apparatus embodying the present invention illustrating its manner of use;

Fig. 2 is a longitudinal vertical section of a portion of the apparatus shown in Fig. 1;

Fig. 3 is a section taken on line IlIIII of Fig. 2; and

Fig. 4 is an end elevation of the portion of the apparatus shown in Fig. 2.

Referring to the drawings, the apparatus of the present invention has two portions, a heat exchanger portion H (Fig. 1), and a blower portion B. The heat exchanger comprises a cylindrical metal casing 10 closed at one endby a Wall member 12 of inorganic refractory heat insulating material. The member 12 is secured to the casing by three screws 14 (Fig. 4). A second wall member 20 of heat insulating material is disposed within the casing 10 in spaced relation with the member 12 and there secured by screws 22. The member 20 is formed to provide air entrance ports 24 adjacent to the casing 10. Within the chamber defined by the casing 10 and the two members 12 and 20 are disposed a plurality of metallic tubes 28, 30, 32 and 34 nested coaxially with the casing 10. The tubes are mounted to provide serially communicating passages by means of an annular end plate 36 to which are welded one end of the tubes 28 and 32 and by a second annular end plate 38 to which are welded one end of the tubes 30 and 34, the plates 36 and 38 being secured respectively to the members 20 and 12 by means of bolts 40 and 42. By this means the tubes are supported entirely in heat insulated relation to the casing 10.

The innermost tube 34 is in communication, by way of a passage 44, with a nozzle 46 threaded into the member 12. Thus air introduced through the ports 24 is caused to flow in a series of passes in alternate directions through the train of passages formed by the tubes and the casing until finally it passes out through the nozzle.

To heat this air, an electrical resistance heating element 5%! is disposed in the space between the innermost tube 34- and the next adjacent tube 32. The heating element is of the sheathed conductor type comprising a resistance heating wire supported within a metallic tube by means of electrical insulating material such as magnesium oxide. The heating element has a circular cross section which is substantially equal to the space between the tubes 34 and 32 and the heating element is helically wound in a single layer about the tube 34 so that air passing between tubes 32 and 34 (leftward as shown in Fig. 2) is induced by it to follow a helical path about the tube 34 with maximum mixing and heat transfer. It will be observed that the tubes 32 and 34, being next to the heating element, will be heated directly thereby and their temperature will accordingly be the maximum attained by any part of the heating assembly other than the heating element itself. Thus the air is caused to traverse an extended path between maximally heated surfaces before leaving the gun and is not cooled by subjection to a relatively cooler metallic surface before it passes through the nozzle 46, while concomitantly, such increased heat transfer at the interior leaves less heat to be absorbed in the outer passes or lost.

The resistance heating wire within the heating element 50 terminates at two points 52 and 54 therein approximately adjacent to the open or left end (Fig. 2) of the tube 34 to the left of which points low resistance conductors 56, 58 continue the electrical circuit beyond the points 52 and 54. These conductors 56, 58, which are therefore relatively cool during operation of the blower, are clampingly supported within the member 20 by set screws 60, 62 from which member they extend to a switch box 64.

Means for supplying air under pressure through the ports 24 to the chamber within the casing 10 comprise a blower including a housing 70 having an exit port with a flange 72 connected by screws 73 to a collar 74 welded to one end of the casing 10. The housing 70 also carries on its exterior an electric motor 76 to which is connected an impeller 78 within the housing.

The motor has leads extending to a junction box 80, the switch box 64 carrying a manually operable switch connected to the motor and to the heating element so that electric power thereto may be switched on and off simultaneously. The impeller is enclosed by means of a cover plate 82 afiixed to the housing 70 by means of screws 84.

In operation the operator actuates the switch at the switch box 64 to supply electric current to the motor 76 and to the heating element 50. The motor rotates the impeller 78 to drive air into the casing 10 whence it is conducted in a series of alternately directed passes and finally out the nozzle 46. During the operation of the blower, the casing 10 which is insulated from any metallic heat conducting connection with the electrical heating element or the directly heated tubes, remains substantially at room temperature so that no exterior or interior insulation, other than that within the metallic sheath of the heating element is required and the blower attains thermal equilibrium in a very short time. Furthermore, problems arising from vibration, corrosion and rapid oxidation of exposed heating wires are largely avoided.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. In a heat blower, in combination, a cylindrical metal casing, two wall members of heat insulating material secured to said casing in spaced relation and defining a chamber therebetween, a plurality of metal tubes of difierent diameters supported within said chamber in nested relation coaxially thereof, said members and tubes being arranged to establish a train of serially communicating passages, a nozzle connected to the innermost tube, means for supplying air under pressure to the outer portion of the chamber, and an electric resistance heating element of the metallic sheathed conductor type disposed in the space between the innermost tube and the next adjacent tube.

2. In a heat blower, in combination, a cylindrical metal casing, two wall members of heat insulating material secured to said casing in spaced relation and defining a chamber therebetween, a plurality of metal tubes of different diameters supported within said chamber in nested relation coaxially thereof and arranged for support alternately from opposite ends to establish a train of serially communicating passages while maintaining a readily separated construction for cleaning purposes, a nozzle connected to the innermost tube, means for supplying air under pressure to the chamber, and an electric resistance heating element of the metallic sheathed conductor wire type wound in a single layer helix about the innermost tube.

3. In a heat blower, in combination, a cylindrical metal casing, two wall members of heat insulating material secured to said casing in spaced relation and defining a chamber therebetween, a plurality of metal tubes of dif-- ferent diameters supported within said chamber in nested relation coaxially thereof to establish a train of serially communicating passages, a nozzle connected to the inner-- most tube, means for supplying air under pressure to the chamber, and an electric resistance heating element:

of the metallic sheathed conductor wire type wound in a single layer helix in substantial contact with and about the innermost tube, the thickness of said element being substantially equal to the space between the innermost tube and the next adjacent tube.

4. In a heat blower, in combination, a cylindrical metal casing, two wall members of heat insulating material secured to said casing in spaced relation and defining a chamber therebetween, a plurality of metal tubes of diflerent diameters supported at one end only alternately by one and the other wall member in nested relation Within said chamber coaxially thereof to establish a train of serially communicating passages, while maintaining a readily separated construction for cleaning purposes a. nozzle connected to the innermost tube, means for supplying airunder pressure to the chamber, and an electrical resistance heating element of the metallic sheathed conductor wire type disposed in the space between the innermost tube and the next adjacent tube, the thickness of said element being substantially equal to the space between the innermost tube' and the next adjacent tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,439,340 St. Clair Dec. 19, 1922 2,028,095 Tully et al. Jan. 14, 1936 2,609,477 Borda et al. Sept. 2, 1952 

